Lipofuscin is a complex lipid/protein aggregate formed in the retinal pigment epithelium (RPE) of the eye as nondegradable end products from phagocytosis of shed photoreceptor outer segments [7]. Lipofuscin granules are considered to be toxic to the RPE and thought to contribute to the pathogenesis of age-related macular degeneration (AMD) [8,9]. Rapid accumulation of lipofuscin and maculopathy can lead to conditions such as Stargardt disease, in which a lack of functional ABCA4 is evident (ATP-Binding Cassette, subfamily A, member 4).
Instruments such as optical coherence tomography (OCT) [1,2] and retinal auto-fluorescence (AF) imaging [3,4] are important imaging modalities in both ophthalmic clinics and research, each capable of imaging different aspects of the retina. OCT is a low-coherence interferometry based imaging modality and primarily provides structural imaging of the retina with microscopic depth resolution. Because lipofuscin is the major source of AF, it can be assessed by monitoring retinal AF. Retinal AF imaging maps the distribution of lipofuscin in the RPE.
AF signals emitted by lipofuscin travel through different retinal layers and the anterior segments of the eye before reaching an imaging receiver. The fluorescent signals will therefore be affected and attenuated by those layers, which can have different optical properties.
Existing retinal AF technologies do not take into consideration the attenuation of fluorescent signals by the media present in their optical path. Thus, the AF images by existing technologies do not accurately reflect the true level of AF in the RPE. Additionally, because the optical properties of the media in the optical path may differ among different individuals, as well as at different ages and pathological conditions in the same individual, it is difficult to compare images from different individuals and in the same individual at different times by using existing AF imaging technologies.